Exposing Meteors Brilliantly, Part 1: Preparing

April 27, 2013

I recently posted a gallery containing a number of photographs of the Geminid Meteor Shower, and a reader asked me to explain how I took the shots. I’m happy to share my knowledge when I can, so here is my first installment of knowledge center articles on astrophotography!

Meteor photography falls under the broader bucket of Astrophotography, which has to do with all things about the night sky:

Wide Field Skies

Startrails

Constellations

Meteors and Bolides

Comets

The Moon

Eclipses (both solar and lunar)

Planets and their Satellites

This form of astrophotography usually requires a moderately powerful telescope

Narrower apertures are usually acceptable, f/10 or narrower are often used

Deep Sky (nebula, galaxies, clusters, star closeups)

This form of astrophotography requires a powerful telescope

The widest aperture possible is usually necessary, f/10 is the minimum, with f/6 or f/4 being much better

Having a flat field can be very important

I will write more on astrophotography as I explore it more. Astronomy has always interested me, even as a child, and I had a couple of telescopes as a kid and teen. I’ve had my eye on the Celestron 11″ EdgeHD Schmidt-Cassegrain telescope for a while, to fulfill both my astronomy and deep sky astrophotography goals. It is a hefty piece of equipment, clocking in at a cool four grand, however its price has steadily been dropping (a year ago it was $4999, today it is a thousand less.) Until I am able to purchase all the necessary equipment to support proper deep sky astrophotography (particularly nebula…I love nebulas), I try to satisfy myself with wide field astrophotography. That generally includes the whole night sky, although frequently that involves night skies with the Milky Way clearly visible. The moon is also a favorite subject, as are comets (when they are visible…lately a lot of comets have been southern-hemisphere only, although we are supposed to get quite a show from Comet ISON later in 2013!)

Meteor showers are also another astronomical favorite, and many of them occur each year. The most recent major show was the Geminids, which occur during the first couple weeks of December, usually peaking around the 14th to 16th of the month. The first thing to know about photographing meteor showers is to make sure you are in a good zone. When meteor showers occur, they are not visible from everywhere…weather obviously plays a role, as does your ability to actually see the radiant source. The radiant is the point in the sky from which a meteor showers meteors appear to originate from. The radiant is usually a star or part of a constellation, and usually named after such. The meteors do not actually come from the namesake of the radiant source…most often they are the particulate left behind by the passage of comets, or sometimes (much less commonly so) by the passage of an asteroid. When the Earth’s orbit takes us into conflict with the orbits of the source entity is when meteor showers occur.

There are several major, persistent meteor showers each year. The most well known of these are the Perseids, Orionids, Leonids and Geminids. These occur from August through December each year. The Perseids are the most well known of the meteor showers, they are usually a spectacular display with maximum rates (ZHR, Zenithal Hourly Rate) of around 100 fairly consistently (this is very good for a meteor shower, if you are lucky to be one where the zenith of the radiant is directly over you). The Orionids are also a good show, occurring in October, with the radiant near the constellation Orion, although its hourly rates are lower, sometimes much lower, than the Perseids. The Leonids are the next major show, occurring in November, and can often put on as spectacular a show as the Perseids, sometimes even more spectacular with multiple bolides (particularly bright meteors that explode as they burn up in the atmosphere, sometimes resulting in meteorites.) The last major show of the year are the Geminids, occurring in December, with maximum rates as high as 200 per hour, and usually over 100 per hour. The Geminids originate from an asteroid rather than a comet, resulting in a different “nature”…the Geminid meteors tend to be slower, with longer trails, sometimes lingering in the sky for several seconds before burning out. Their trails can be quite bright, but due to their slower speed, the show overall is sometimes not quite as spectacular as the others.

There are a number of other meteor showers each year. Many are inconsistent, others are not as spectacular as the major four. Some, on the other hand, can be even more spectacular. A couple to keep an eye out for are the Quadrantids (an intense shower that lasts for a short period of time during January), and the Draconids (a fainter meteor shower in August, however its maximum rates can reach as high as 1000 meteors per hour, or 16 meteors per minute, one every few seconds). A number of other smaller showers occur each year, some with variable intensities, most with very faint meteors. Faint meteors do not make for great astrophotography unless you have a powerhouse of a camera with very clean very high ISO capabilities (such as a Canon 1D X, or maybe a Canon 5D III or Nikon D4.) For someone just starting out, I would say the two best showers each year are the Perseids and the Geminids, with the Geminids taking the forefront thanks to their longer trails in the sky.

When planning to view a meteor shower, it is best to scout out a good location before anything else. Meteors are quick, and while they can be momentarily bright, other brighter or more expansive sources of light can often drown them out. The moon, for one, can often be a “hazard” to meteor viewing if it will be bright and in close proximity to the radiant source at the time the shower peaks. Worse than the moon, however, is our own man-made problem: light pollution. The very lights from our sprawling cities and suburban areas can contaminate viewing conditions, greatly reducing the visibility of the night sky in general, and limiting the number of meteors you’ll be able to photograph or see. (Light pollution occurs when light from all our artificial nighttime illumination scattering off of particulates in the air, which are often higher in cities thanks to human activity, particularly vehicle exhaust. The photo featured on this article demonstrates the impact of light pollution…even over thirty miles from the nearest suburban area, and fifty miles from downtown Metro Denver, light pollutes the majority of the frame with its yellow bubble, blotting out the stars, and swallowing smaller meteors.) One needs DARK skies for proper meteor viewing, and the darkest skies possible to photograph the majority of them. Getting well out of any city and suburban area, out into the wilderness as far as you can go, will maximize the potential umber of meteors per hour you’ll see, and improve your chances of photographing them. Burying yourself in a valley in the mountains, or heading out 100 miles from anything, should be sufficient to achieve ideal conditions, although 30 to 50 miles will suffice in a pinch.

Before you head out to watch or photograph a meteor shower, it is best to know if the radiant source will reach its zenith when the shower peaks or not, and if not, whether the radiant source will be sufficiently visible from your intended viewing location. Weather is the first thing to look out for…clouds will certainly put a damper on any photography, and reduce the visible rates to as little as a couple per hour, if any at all under a fully overcast sky. Also check to see if the radiant source might fall behind treetops or mountain ranges during its peak, as that would also diminish the visible rates. Ideal viewing occurs when the radiant source is directly overhead when the shower peaks, which would mean it is within a 45 degree range directly overhead during the bulk of the showers most spectacular time. Note that meteors for the major showers tend to start days in advance, and will linger days after the peak, although at considerably lower hourly rates. As you approach the peak day(s), rates will often climb. If you know you’ll have bad weather or poor viewing conditions on the day and time the shower peaks, you might want to head out early and see what you can see, photograph what you can photograph.

Last thing to do before heading out is make sure you have the right equipment. First and foremost, a DSLR with a fast wide angle lens is best. DSLR cameras have large sensors with large pixels and good low light sensitivity. Your average “point and shoot” camera might suffice in a pinch, but noise might drown out any detail other than the meteor itself unless you have a particularly good one. Mirrorless cameras, so long as you can use at least an f/2.8 lens at a wide angle, should also work well. When it comes to the lens, shorter focal lengths are better, and wider maximum apertures are better. For the average DSLR, you want a lens to be 24mm long or shorter. I personally usually use 16mm. If you have a fisheye lens, they can produce excellent images with an added twist, and a lot of wide field astrophotographers use nothing but fisheye lenses for the warped, ultrawide field effect. The fastest aperture you can get your hands on is ideal. I would say no smaller than f/2.8, however f/1.8 or even f/1.4 if you can manage it will be better. You will usually stop down just a little to sharpen things up, and an f/1.4 lens at f/2 can be quite sharp, and faster than any other option.

Aperture is critical when it comes to astrophotography…the bigger the aperture, the more light you get on the sensor. It should be noted that the ISO setting on a camera is often a misinterpreted feature. It is often called “sensitivity”, however that name is a misnomer. Increasing ISO does not actually increase the sensitivityof the sensor, or in any way allow the sensor to gather more light than it does at ISO 100. Increasing ISO simply amplifies the signal that was received. The only way to get more light is to get more light, and a wide aperture does that. You won’t be using f/8, or likely even f/5.6, when it comes to astrophotography, and that rule stands for meteors. You might find yourself stopping down to f/4 if you have a lens with particularly poor quality wide open, but generally speaking, assuming you have a problem with the quality of the stars at maximum aperture, you won’t want to stop down more than two thirds of a stop, maybe a stop at most. Sharpness is not really something that matters in this context…light is really all that matters. More light, brighter image, less noise.

When it comes to image noise, the bigger the pixels, the better. I mentioned DSLR cameras before. The biggest benefit of a DSLR is the larger sensors. Most DSLRs come in two varieties: APS-C and Full Frame (FF), referring to the size of the sensor. A DSLR with an APS-C sensor has a sensor about 22-25mm long. A DSLR with a FF sensor has a sensor 36mm long. Assuming you have an 18mp DSLR, if it is APS-C, the pixels will be 4.30 microns in size, and if it is FF, the pixels will be 6.95 microns in size. The larger the pixel, the less noise your image will have overall, especially at higher ISO settings. When it comes to wide field astrophotography, the ISO setting you need to use will ultimately depend on the equipment and goals. Single-shot wide field astrophotography often demands ISO settings around 800 to 1600. When photographing meteors, you will probably want to use ISO 3200 at least, possibly even ISO 6400 or more if your camera supports it, and depending on the intensity of the meteors.

The best camera on the market right now for astrophotography, from a price to value standpoint, is probably the Canon 6D. It has big pixels, is full frame, offers a nice balance between pixel count and pixel size (20mp) and has very good high ISO performance. The high ISO performance is on par, if even slightly better, than the Canon 5D Mark III. The price point is decent, and if you can find it on sale, can be excellent for what your get (price drops have been seen into the $1800 range, and at its cheapest, was ~$1650, a real steal for a full-frame camera.) If you cannot buy a camera to suit your astrophotography needs, any DSLR will do just fine, even an entry-level Canon EOS 650D or a Nikon D5200, which should cost less than $1000. An older generation entry-level DSLR, many of which can be picked up for $400-$500, will also suffice. For cheaper lenses, you might look to Sigma, Tamron, or Tokina, particularly the wider angle zoom lenses, but remember to get a lens with at least an f/2.8 maximum aperture. If you have some money to spend, especially if you get a Canon 6D or 5D III, then you should look at better lenses. The Canon EF 16-35mm f/2.8 L II is a great zoom lens, as is the EF 8-15mm f/4 L lens (despite the narrower aperture, it has excellent quality wide open, and f/4 is still sufficient…plus, it is the only way to get that fisheye look if that is what your after.) From a prime lens standpoint, the 14mm f/2.8 L, 24mm f/1.4 L, 24mm f/2.8, 28mm f/1.8, 28mm f/2.8, and possibly the 35mm f/1.4 L and 35mm f/2 lenses will all serve you well (although the L-series lenses will cost you, possibly more than even the 6D itself.)

A couple of other accessories will also be necessary to get good meteor shots. A sturdy tripod is one…the exposure times for wide field night sky work, even at a higher ISO like 3200, will be several seconds. You can’t hand-hold the camera for this kind of work. Any tripod will do, however carbon fiber tripods tend to be the most stable…Gitzo or Really Right Stuff make some of the better ones, and their prices range from a few hundred dollars to over a thousand dollars. You’ll want an easy to use tripod head, and a basic ball head will usually do. A tripod is usually the only thing you need besides the camera for standard wide field work. When it comes to meteors, you will want one other tool: an intervalometer. Trying to time your photos right to capture meteors can be difficult. If your camera has a built in automatic timer that repeats on an interval, your good to go. Most cameras do not have such a feature, so you’ll want to pick one up…you can find them at Amazon.com. Finally, if you really want to maximize your chances of getting good meteor shots, you will probably want to double up on your kit…two cameras, each with their own tripod and intervalometer. You can cover a greater area of the sky this way. Another option is to simply go out with friends, and get as many cameras pointed at the sky as you can. When the radiant source is at its zenith, the entire hemisphere of the sky is effectively fair game for a meteor…an off-axis radiant source will usually limit the area of the sky where meteors are likely.

My personal kit is currently the Canon 7D with the EF 16-35mm f/2.8 L II lens, usually at the wider end of the range, although at times I’ll use 24mm and 35mm to unclutter my scene and just get the stars. I use a PIXEL intervolometer, and a Gitzo GT3532LS tripod. I wouldn’t recommend the 7D for astrophotography these days…it is becoming rather dated technology, and even when it was first released over four years ago, it had a few problems with noise. It is an excellent camera when you have lots of light, and does a superb job for birds, wildlife, even landscapes. In the future, I’ll be using a Canon 5D III for my astrophotography, both wide field and eventually paired with a Celestron telescope for deep sky stuff. From a value standpoint, I really do think the 6D strikes a supreme balance between pixel size, pixel count, and price…you can’t go wrong with the 6D for night sky work, and as an added benefit it has extremely low light AF capabilities that might help you get clean focus on those dim stars.

In part 2 of this article, I’ll go into the details of wide field astrophotography, and cover the one key trick that will help you get stellar meteor photos that outshine everything (puns intended)!